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Archived

Avalanche Forecast

Feb 28th, 2017–Mar 1st, 2017
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
1: Low
The avalanche danger rating below treeline will be low
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
1: Low
The avalanche danger rating below treeline will be low
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
1: Low
The avalanche danger rating below treeline will be low

Regions: Northwest Inland.

Cranking winds accompanied by 5-10 cm will likely build new and reactive wind slabs at upper elevations. Deeper slabs may exist on leeward slopes.

Confidence

Moderate - Wind effect is extremely variable

Weather Forecast

Wednesday: Cloudy with some sunny periods and  moderate-strong (60 km/h) SW winds. Alpine temperatures high of -10.Thursday: Snow 5-10 cm with strong SW winds. Alpine high of -6 and freezing levels 900 m. Friday: Mix of sun and cloud and a trace of new snow. Moderate- strong ridgetop winds from the SW.

Avalanche Summary

On Monday, no new avalanche activity was reported. On Sunday, numerous natural wind slabs were reported up to size 1.5 which were triggered by the recent wind event. With forecast snow and strong winds reactive wind slabs are likely over the next several days.

Snowpack Summary

New snow 5- 15 cm is slowly burying a plethora of old snow surfaces including isolated wind slabs and wind press, sun crusts, and surface hoar. The new snow may have a poor bond to these interfaces. A layer of surface hoar that was buried on February 10th may exist 30 to 60 cm below the surface, but there's a fair bit of uncertainty regarding the reactivity and distribution of this layer. A stiff mid pack sits above weak sugary snow near the ground. Although possibly dormant, this basal weakness has the potential to produce very large destructive avalanches especially in shallower snowpack areas. Below 1000 m a strong supportive rain crust exists.

Avalanche Problems

Wind Slabs

Changing wind directions and new snow will build fresh wind slabs on N-NE aspects. Old wind slabs may continue to linger on southerly aspects due to the recent winds out of the North.
If triggered the wind slabs may step down to deeper layers resulting in large avalanches.Use ridges or ribs to avoid pockets of wind loaded snow.

Aspects: North, North East, East, South East, South.

Elevations: Alpine, Treeline.

Likelihood: Possible - Likely

Expected Size: 1 - 2

Deep Persistent Slabs

A lingering weakness at the bottom of the snowpack may remain sensitive to human triggering, especially in shallow snowpack areas. Smaller avalanches in motion also have the potential to step down and trigger deep persistent slabs.
Avoid steep convexities or areas with a thin or variable snowpack.Be aware of the potential for full depth avalanches due to weak layers at the base of the snowpack.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Unlikely

Expected Size: 2 - 4